Field emission displays (FED) are among the most promising candidates for the next generation of displays. Field Emission Backlights for liquid crystal displays (LCD) also attract the interest of many researchers today.
One well-known type of electron emitter structure of a FED, a Spindt type emitter, is shown schematically in FIG. 1. A lower portion of the emitter comprises a glass substrate 1, covered by a lower electrode 2. A number of insulator elements 3 support gate electrode elements 4. This type of emitter has a small Mo cone 5, in electric contact with the lower electrode 2, as a cathode. When a large enough negative voltage is applied to the cone 5 (via the lower electrode 2) the electric field concentration at the top of the Mo cone 5 becomes high enough to expel electrons. The electrons are attracted across a gap to an upper portion of the FED, composed of an upper electrode (anode) 7, which is sandwiched by a phosphor layer 6 and a second glass substrate 8. The generation of light by the phosphor layer 6 can be controlled by controlling the voltages applied to the gate electrode elements 4, in particular so as to make certain areas brighter than others. If the gate elements 4 are omitted, the structure generates uniform light, and may also for example function as a uniform field emission backlight of an LCD.
This emitter array is fabricated using vacuum-processing machinery in a photo-lithographic process which needs many masks. The Mo cone 5 is deposited with the substrate tilted, and then by rotating it. The series of process steps is very complicated and expensive, and it is difficult to make exactly the same cone shape for each of the many emitters in the array, which leads to uneven electron emission properties.
Another type of emitter, a Carbon Nano Tube (CNT), also attracts much interest. FIG. 2 shows a schematic diagram of the CNT type FED. Elements having the same meaning as those in FIG. 1 are denoted by the same reference numerals. The only difference is that a plurality of CNTs 9 are used as each cathode.
The CNTs are grown perpendicular to the surface of the substrate 1 and the electric field concentration is high at the top of the CNTs. Carbon is well known for its high electron emission property, so CNT is a suitable material for an electron emitter. However, the CNT are normally grown in a vacuum and usually high temperature is required to make good quality CNTs, so the process is expensive, and the substrate also expensive because it has to withstand high temperature during the process.
To solve the CNT-related problems which are mentioned above, some researchers have proposed a binder having the consistency of a paste and containing independent CNTs. Such a binder is pasted onto the substrate in place of the CNT of FIG. 2, and some of the CNTs in the paste happen to project above the binder surface, and work as cathodes. Unfortunately, this method makes it difficult to achieve even electron emission in the array, and also there is also high contact resistance between the electrode 2 below the CNT paste and each CNT. Additionally, the independent CNTs themselves are an expensive material.